Original
Unmetamorphosed
rock
Nucleation of new
minerals
in response to
changes
in T or P or both
Different stages of
mineral growth
involve both
textural and
mineralogical
changes
Ions migrate either
by solid state diffusion or
Intergranular fluids
A
B
C
SiO2 + CaCO3 ïƒ CaSiO3 + CO2
Deformed metamorphic rocks
Types or Envs. of metamorphism
• Contact (thermal) metamorphism =
around magmas
• Regional metamorphism = along
subduction zones in areas of mountain
building. Rocks in these setting are
subjected to both increase in T and to
directed pressures.
Subduction zone and
regional metamorphism
Agents of metamorphism
• Heat = thermal energy- geothermal
gradient
• Pressure increases at a rate of about 250-
300 bars/km of depth.
• Chemical active hot fluids (H2O, CO2 are
the most common) moving within the rocks
are capable of dissolving rocks and
precipitating others at other places
Types of Metamorphism
Contact metamorphism
– Heat
– Chemical fluids from an igneous body
– Alter rocks adjacent to the magma
Regional metamorphism
– Large, elongated area
– Tremendous pressure
– Elevated temperatures
– Fluid activity
– Occurs at convergent and divergent plate
boundaries
Confining pressure=analogous to
hydrostatic pressure
Differential stresses = directed
pressures
Textures
• Foliated
rocks
• = regional
• Metamorphic
• rocks
